1. Field of the Invention
The present invention relates in general to a self-administration device for liquid medicines, and in particular to an improvement to a liquid medicine self-administration device that enables a patient to self-administer a liquid medicine such as an analgesic or anesthetic.
2. Description of the Related Art
In the field of anesthesiology, administration of liquid medicines by an epidural catheter insertion method employing a low-dose continuous injection instrument has come into use in recent years as a way to alleviate pain such as postoperative or cancerous pain. However, due to variability in medical condition or constitution among patients, there will be instances in which a patient may report sudden severe pain despite being continuously administered a low dose of an analgesic. Accordingly, currently in development are liquid medicine self-administration devices which allow a patient to self-administer a large dose of an analgesic in a single shot in order to rapidly treat such occasional symptoms.
Given this background, the Applicant previously proposed a liquid medicine self-administration device having a number of outstanding features (see U.S. Pat. No. 6,213,981). This liquid medicine self-administration device includes a cylindrical housing (casing) wherein a base member (port portion) having a liquid medicine inlet/outlet port and capable of flexural deformation is attached fitting into one open end of the housing, and pushing means is inserted into the other open end so as to be slidable in the axial direction. Within the housing there is accommodated a reservoir of pouch form that, when arranged with an opening thereof communicating with the liquid medicine inlet/outlet port of the base member, is closed by the base member and retains liquid medicine that has been injected through the liquid medicine inlet/outlet port. By then sliding the pushing means, through flexural deformation of the reservoir induced by being pushed by the pushing means, the liquid medicine retained within the reservoir will be expelled through the inlet/outlet port. Using this liquid medicine self-administration device, the patient can push and slide the pushing means in order to self-administer a one-time large dose of a liquid medicine containing an analgesic or the like.
With such a liquid medicine self-administration device, the pushing means in particular is composed of a cylindrical operating member (operating member) that has been slidably inserted into a first open end of the housing, and a spring member housed inside the operating member and adapted to undergo elastic deformation when the operating member is slid towards the base member end. Engaging means is also provided for engaging (locking) the operating member when the operating member has reached a slide end position situated at the base member end, so that the operating member is non-slidably locked. With the operating member in the locked state, the reservoir will undergo pressure deformation due to the restoring force of the elastically deformed spring member.
Using such a liquid medicine self-administration device, the patient need merely push the operating member until it is locked by the engaging means; subsequently, through the restoring force of the spring member, the liquid medicine that was retained in the reservoir will be administered to the patient automatically under constant pressure. For this reason, in contrast to the case where a conventional liquid medicine self-administration device lacking such engaging means is used, it is unnecessary for the patient to continue to push the pushing means until the entire amount of liquid medicine inside the reservoir has been completely expelled, and it is also possible to avoid abrupt expulsion of liquid medicine from the reservoir due to the pushing means having been pushed with excessive force. Consequently, through the use of the proposed liquid medicine self-administration device, even a patient with diminished physical strength will be able to self-administer liquid medicine in a stable and reliable manner, and it will be possible to effectively prevent liquid medicine from leaking due to being expelled too abruptly.
The liquid medicine self-administration device has been designed so that, through a manual operation performed after the liquid medicine in the reservoir has been expelled to release the operating member from the locked state of engagement by the engaging means, the reservoir will recover to its condition prior to deformation through the pressure of injection of liquid medicine into the reservoir. In association with the recover of the reservoir, the operating member will return from the slide end position to its position prior to being pushed. Thus, in the event that the patient has forgotten to perform the unlocking operation, it will be necessary to perform unlocking and to then wait until the reservoir has refilled with liquid medicine before the next shot of liquid medicine can be administered.